The AROS distribution Icaros Desktop has made its next step towards compatibility with legacy Amiga workbench applications, including an entire AROS enviroment compiled for the classic Amiga platform, which is almost binary compatible with the original Amiga OS 3.1 (and its extensions). When the user needs an old program, he or she only has to fire up the AROS M68K environment and run the application. The Amiga virtual machine can optionally be set to run at startup like a system service.

AROS is still missing large chunks of functionality. Eg. the standard GUI since 1999 is ReAction, this is not supported at all by AROS, neither are OS3.5/3.9 API calls.

Standard, de facto GUI for Amiga OSes has ever been MUI. The ReAction path has been followed and endorsed by Hyperion, but most applications - even "NG" ones - use MUI and can be supported by AROS' Zune MUI clone.

" AROS is still missing large chunks of functionality. Eg. the standard GUI since 1999 is ReAction, this is not supported at all by AROS, neither are OS3.5/3.9 API calls.

Standard, de facto GUI for Amiga OSes has ever been MUI. The ReAction path has been followed and endorsed by Hyperion, but most applications - even "NG" ones - use MUI and can be supported by AROS' Zune MUI clone. "

Good point, MUI has been king since the 90s. Does this count for OS 4.x apps as well though? I was under the impression MUI was now a MorphOS/AROS(Zune) thing and that OS 4 didn´t get support?

Might be totally off the mark though, as I only keep an eye on AROS of the NG platforms nowadays.

OS4 does have a native port of MUI which is distributed with it, but it's not the "standard" toolkit. You'll find that most OS4-only programs are Reaction-based, whereas programs which are ported from other Amiga-ish platforms tend to use MUI. Also, if you're writing some software for OS4 or any of the platforms and want to port it to the others, your best bet is to start with MUI as it's common across AROS, Morphos, OS4 and classic.

Good point, MUI has been king since the 90s. Does this count for OS 4.x apps as well though? I was under the impression MUI was now a MorphOS/AROS(Zune) thing and that OS 4 didn´t get support?

Yes, this does count for OS 4.x too. People, who want to write software that will run on OS 4.x only, will probably use ReAction; people who try to make their applications "cross-compatible" between (and available on) all Amiga "heirs" will prefer MUI. Efforts are in progress to bring AROS' Zune to the same features level of MUI 3.8, in order to enhance this side of compatibility as well.